The proposed research involves development of a specialized near infrared spectroscopy (NIRS) instrument for use as a diagnostic tool in evaluation of erectile dysfunction. The research represents an extension of work completed during the Phase I component of the project. The hypothesis being tested is that the dynamics of blood volume changes in the penis have diagnostic significance and that determination of these by a simple spectrophotometric technique will have an impact on the management of vasculogenic impotence. The specific aims of the Phase II study include refinements in design and construction of the NIRS instrument with a focus on its clinical applicability and simple use, and performance of extensive clinical studies to validate the technology. Refinements in optical probe design and simplification of instrument operation will be made to improve the practical use of the equipment along with development of simplified calibration methods and data analysis procedures. Objectives of the clinical studies include establishing the test-retest reliability, reproducibility, normative parameters, and cross validation of NIRS with other diagnostic techniques,commonly used for the evaluation of erectile dysfunction. The basic clinical protocol will involve the simultaneous use of NIRS and other diagnostic methods (nocturnal penile tumescence monitoring, color duplex ultrasonography, penile tonometry, and clinical assessments) to evaluate the extent and time course of blood volume changes during the erection cycle in both healthy volunteer subjects and in patients with various degrees of erectile dysfunction. Both pharmacological and physiological methods will be used for induction of penile erection, including intracavernous injections of vasodilators, visual sexual stimulation and sleep-related erections. Volunteer subjects will represent specified age ranges, and patients will include various specific etiologies for erectile dysfunction, including diabetes, cardiovascular disease, neurological disease, and non-organic (psychogenic) disease. Findings from these studies can be expected to determine the utility of NIRS as a means of diagnosing erectile dysfunction easily and effectively, thereby suggesting the widespread use of NIRS for this purpose. PROPOSED COMMERCIAL APPLICATIONS The proposed research will lead to development of a specialized NIRS instrument to be used both by general urologists in the professional office environment as well as specialists at male sexual dysfunction clinics for medical evaluation and management of erectile dysfunction.